This invention relates to an economical method for improving the strength of a water-saturated soft soil.
It is generally known from the past to improve the strength of a water-saturated soft soil deposited on the bottom of seashore, river, lake and lagoon so as to enable passage of people or traffic vehicles and conveyance of construction machines on reclaimed soft grounds formed by dredging such water-saturated soft soil. A method wherein a strengthening agent or solidifying agent is used is known as a method for improving the strength of such water-saturated soft soil. In this method, cement, quick lime, water glass, asphalt and organic macromolecular substances are used as the strengthening agent. However, these strengthening agents are not satisfactory since they are poor in strength-improving effect or are economically unattractive. Especially, in case of a large-scale treatment of such soft soil of a high water content such as a certain kind of sludge or mud called "hedoro" deposited on the bottom of a river or seashore, the amount of such soft soil to be treated in one batch reaches several thousand to several million cubic meters, thus requiring an extremely large amount of the strengthening agent. Hence, the utilizable strengthening agent must be as cheap as possible and must be one capable of remarkably improving the strength in smaller amounts.
In Japanese Unexamined Published Patent Appln. No. 141459/76 there is disclosed a method wherein a mixture of a cement and gypsum is used as a strengthening agent for the soft soil. The strengthening agent disclosed in this reference exhibits an enhanced strength-improving effect to the water-saturated soft soil as compared with a cement alone or a mixture of a cement and quick lime, but is still unsatisfactory in practical use so that a larger amount of the strengthening agent and a longer period of time are required to treat a highly water-saturated soft soil so as to have a practically acceptable strength. This reference suggests the optional use of a water-granulated iron blast furnace slag or fly ash in addition to a cement and gypsum as indispensable ingredients. However, both the water-granulated iron blast furnace slag and the fly ash are not indispensable but optional in this prior art method in view of the proportion defined therein as 0-30%. In this reference, the water-granulated iron blast furnace slag is regarded equivalent in function to the fly ash which is very poor in strength-improving effect and no discussion is made on the properties and technical effects of these optional ingredients. Thus, these ingredients are recognized in this reference only as filler or the like additive for the reduction in the cost of the indispensable strengthening agents. Anyway, this reference fails to teach an effective means for furnishing water-saturated soft soil with satisfactory strength.